Bishtina Mohammed El Salam of the Misseriya, one of two dominant tribes in Abyei, said his people will not accept joining the south following the Jan. 9 referendum.

His tribe shares the region with the Dinka, who say they want to join the south.

"If the Dinka take this decision - to annex Abyei to the south - there will be an immediate war without any excuse," El Salam told Al Jazeera. "We think they should be reasonable and think about it. They should know that those who are pushing them to take that decision will not give them any back-up."

Under a 2005 peace agreement, a separate referendum is to be held for Abyei's people to opt to join the north or the south.

But issues over borders and residency rights have delayed that vote, which was due on Jan. 9.

Al Jazeera's Mohamed Vall, reporting from Abyei, said there is a situation of mutual fear between the two tribes in the region.

"The Dinka have been talking about a local referendum they are going to organise on their own outside the framework of the peace agreement between the north and the south," he said.